Power slip

ABSTRACT

A power slip that utilizes modified SDXL slips and regular drilling bowls that fits to the pin drive master bushings of the rotary table and utilizes the depth of the drive pin holes as part of the actuators, thus allowing the power slip to set lower for added clearance and safety during drilling operations. Cables are anchored to a base plate and slip linkages and slip connectors are pivotally mounted to the slips and to the top plate so that, when the lift cylinders are actuated, the slips are moved to the released position. This two-stage linkage and cable design maximizes the movement of the slip assemblies while minimizing vertical movement of the power slip&#39;s housing. The base plate of the power slip is provided with a plurality of tubular pins adapted for mounting the base plate to the pin master bushing of a rotary table, and a portion of the lift cylinder is positioned in the interior hollow pins to maximize the movement of the slip assemblies upon actuation of the lift cylinders while minimizing the vertical dimension of the power slip.

BACKGROUND OF THE INVENTION

The present invention relates to an improved slip for gripping tubularsin a rotary table to support the tubular from the table. In more detail,the present invention relates to a power slip that provides fullretraction of the slip segments that is of minimal vertical dimensionfor added safety and ease of use. The present invention is particularlyuseful for running drill pipe into and out of a well bore and forrunning casing pipe into a well bore.

There are various situations in which it is necessary or desirable totemporarily support the weight of a drill or casing string with taperedslips received within a tapered slip bowl while an upper joint or standof pipe, or other structure, is being connected to or disconnected fromthe string. To speed the set and release of such slips, a number ofpower slips are available that act to move the slip segments upwardlyand downwardly (relative to a co-acting slip bowl) into and out ofengagement with the tapering camming surface of the bowl, and thereforeinto and out of engagement with the drill pipe or casing joint. Examplesof such slips include the VARCO PS-15 and PS-16 (National Oilwell Varco,Houston, Tex.) power slips as well as those available from Den-Con ToolCo. (Oklahoma City, Okla.).

Although these prior power slips are in current use and function fortheir intended purpose, there are a number of opportunities forimprovements, particularly in connection with their ease of use. Onesuch opportunity for improvement relates to the vertical height of thepower slip, and therefore its size, weight, and ease of installation.More importantly, however, a short power slip provides advantages insafety and clearance.

These advantages of safety and clearance are provided by using pins thatsit down into the holes in the pin drive master bushing to provideadditional vertical stroke for the cylinders that lift the slips to theraised position up and away from the drill pipe or casing, therebyproviding sufficient retraction of the slips while minimizing thevertical dimension of the power slip.

The power slip of the present invention also provides an advantage overknown prior art slips (such as the Varco power slip) in that it utilizesa dual linkage and independent slip assemblies. The dual linkageprovides for additional stroke length in retracting the slips by foldingupwardly upon itself. Independent slip assemblies (as compared to theslip assemblies in known prior art power slips, which are linked with ahinged pin connection, and retract and set the same distance at the sametime) allow the power slip of the present invention to accommodateoff-center drill pipe and/or casing.

Known prior art power slips utilize gravity to cause the slips to fallback into the retracted position. The Varco PS-15 and PS-16 power slips,for instance, are provided with steps on the back of the slip segmentsfor the purpose of facilitating the falling of the slips back from thepipe. The power slip of the present invention, however, utilizes a cableto pull the slips up and back away from the drill pipe and/or casing,thus providing a positive clearance between the tubular and the openingthrough the power slip, all while minimizing the vertical height of thepower slip and maintaining sufficient stroke to fully retract the slipsegments.

It is, therefore, an object of the present invention to provide a powerslip with minimal vertical height that also provides sufficientretraction of the slips to insure that the slips are raised far enoughfrom drill pipe or casing positioned between the slips to providesufficient clearance when in the retracted position while providing theadvantages of safety and clearance off a power slip of minimal height.

Another object of the present invention is to provide a power slip thatuses a modified set of SDXL slip segments (so-called “extra long slips”as known in the art), eliminating the need for a guide ring and allowingfor regular drilling bowls to be used as a back-up for the slips.

Another object of the present invention is to provide a power slip thatdirectly engages the pin drive master bushings of the rotary table,utilizing the depth of the drive pin holes as part of the actuators,thus allowing the power slip to set at a lower height.

Another object of the present invention is to provide a power slip thatfits directly over the master bushing, with no panels or other equipmentextending over the rotary table, reducing the likelihood of possibleinjury and facilitating movement by rig personnel.

Other objects, and the many advantages of the present invention, will bemade clear to those skilled in the art in the following detaileddescription of several preferred embodiments of the present inventionand the drawings appended hereto. Those skilled in the art willrecognize, however, that the embodiments of the invention describedherein are only examples provided for the purpose of describing themaking and using of the present invention and that they are not the onlyembodiments of power slips that are constructed in accordance with theteachings of the present invention.

SUMMARY OF THE INVENTION

The present invention addresses the above-described problem by providinga power slip for releasably gripping a tubular comprising a base plate,a top plate, one or more lift cylinders mounted between the base plateand the top plate for raising the top plate relative to the base plate,and at least two slip assemblies. Each of the slip assemblies comprisesa slip linkage pivotally mounted to the top plate, a slip connectorpivotally mounted to the slip linkage at one end and adapted at theother end for pivotally mounting to a slip segment, the slip segmentreleasably gripping a tubular positioned between slip assemblies, apulley mounted to the top plate, and a cable having one end anchored tothe base plate and the other end anchored to either the slip linkage orthe slip connector, or both the slip linkage and the slip connector, andpassing over the pulley for pulling the slip segment mounted to the slipconnector up and back away from a tubular positioned between slipassemblies when the top plate is raised relative to the base plate.

In another aspect, the present invention provides a method of retractinga plurality of slip segments mounted in a slip from a set positionengaging a tubular positioned between slip segments to a raised positionin which the slip segments are released from the tubular comprising thesteps of actuating a lift cylinder to raise a top plate relative to thebase plate of the power slip, thereby causing the portion of a cableanchored to the base plate that passes over a pulley mounted to the topplate to shorten relative to the top plate, rotating a slip linkage thatis pivotally mounted to the top plate and to which the end of the cablepassing over the pulley is anchored to rotate relative to the top plate,and rotating a slip connector that is pivotally mounted to both the sliplinkage and to a slip segment relative to the slip linkage when theportion of the cable that passes over the pulley is shortened byactuating the lift cylinder. As the slip connector rotates, the slipsegment to which the slip connector is pivotally mounted is raised froma downward, set position to a raised position in which the slip segmentis released from a tubular.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures,

FIG. 1 shows a partially cutaway, partially sectional view of oneembodiment of a power slip constructed in accordance with the teachingsof the present invention in which the slip segments are in a first,released, or up, position.

FIG. 2 shows the power slip of FIG. 1 with the slip segments in a secondposition engaging a tubular extending through the power slip.

FIG. 3 is a top, plan view of the power slip of FIG. 1 with the coverremoved and showing portions of the power slip in cutaway and sectionalview.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In more detail, FIG. 1 shows a first embodiment of a power slipconstructed in accordance with the teachings of the present invention atreference numeral 10. Power slip 10 is comprised of base plate 12 andtop plate 14, the base plate 12 being provided with structure adaptedfor engaging the pin drive master bushings 16 of a rotary table 18 inthe form of the pins 19 that sit down into the insert sleeve 21 that isthreaded into bushings 16 (see also FIG. 2). A central opening 20 passesthrough rotary table 18 and a drilling bowl 22 of a type known in theart is engaged to the inside of rotary table 18.

One or more lift cylinders 24 is spaced radially around the periphery ofthe base plate 12 and mounted between the base and top plates forraising top plate 14 relative to base plate 12 when actuated. As will beapparent to those skilled in the art who have the benefit of thisdisclosure, the lift cylinders 24 may be hydraulic, pneumatic, orspring-loaded (by mechanical springs or air) cylinders. Referring toFIG. 2, it can be seen that the pins 19 received within the pin drivemaster bushings 16 are hollow and that the lift cylinder 24 is actuallylocated in the pins 19 so that the lift cylinder is long enough toprovide sufficient stroke length to fully retract slip segments 30 (asdescribed below) while minimizing the vertical dimension of power slip10 so as to avoid interference with other equipment at the wellheadwhile also increasing safety and ease of use. An adjustable tensioncable 26 is mounted between base and top plates 12, 14 for limitingmovement of top plate 14 relative to base plate 12.

Referring now also to FIG. 3, a plurality of slip assemblies, indicatedgenerally at reference numeral 28, are radially spaced around the baseand top plates 12, 14. In the preferred embodiment shown, three slipassemblies 28 are provided (instead of, for instance, four) so that eachslip segment 30 has a wider face 32 for engaging the outside diameter ofthe tubular (not shown) positioned between slip assemblies 28 andpassing downhole through power slip 10, making it easier to center thetubular on each slip segment 30 and leaving less room between segments30 for the tubular to be damaged or to get trapped off-center. Thoseskilled in the art will recognize, however, that satisfactory functionis obtained in the power slip of the present invention with four or moreradially-spaced slip segments and that, although it would likely notfunction optimally, the power slip of the present invention would becapable of operating with as few as two slip assemblies 28.

Each slip assembly 28 is comprised of a slip linkage 34 that ispivotally mounted to top plate 14 and a slip connector 36 that ispivotally mounted to slip linkage 34 at one end 38 and adapted at theother end 40 for pivotally mounting to a slip segment 30. A pulley 42 ismounted to top plate 14 and a cable 44 having one end 46 anchored tobase plate 12 and the other end 48 anchored to the linkage pin hanger 50passes over pulley 42. Although shown in the preferred embodiment asbeing anchored to the linkage pin hanger 50, those skilled in the artwho have the benefit of this disclosure will recognize that the end 48of cable 44 can also be anchored to either the slip linkage 34 or theslip connector 36, linkage pin hanger 50 providing the pivot pointbetween slip linkage 34 and slip connector 36. In this same regard, inthe preferred embodiment shown, slip connector 36 is provided with anangled portion 37 that provides mechanical advantage and additionalrotation resulting from the pivoting of the slip connector 36. For thisreason, slip connector 36 is described herein as being “J”-shaped, butthose skilled in the art will recognize from this description that slipconnector 36 need not be “J”-shaped to function for its intended purposeand/or that slip connector may be “L”-shaped or shaped in other shapesthat provide the mechanical advantage and additional rotation describedherein.

Referring now to FIG. 2, which shows the slip segments 30 in loweredposition in which they would engage a tubular positioned therebetween,it can be seen that the configuration of the slip assemblies 28described and shown herein causes the slip linkage 34 and slip connector36 to pivot as pulley 42 rotates under cable 44 as top plate 14 israised relative to base plate 12 by lift cylinders 24. The liftcylinders 24 are actuated on the drilling floor by, for instance,stepping on a foot pedal (not shown) that is connected to a valve thatraises top plate 14. A hand valve (also not shown) is also provided atthe driller's panel for actuating (or releasing) the lift cylinders 24.In more detail, upon actuation of the lift cylinders 24 to raise topplate 14, slip linkage 34 is pivoted in the direction of arrow 52 inFIG. 2 by action of cable 44, pulling slip connector 36 in that samedirection. As a result, slip connector 36 pivots relative to sliplinkage 34 in the direction of arrow 54 until the slip connector 34 andslip linkage 36 reach the position shown in FIG. 1. As a result of theaction of this dual linkage, slip linkage 36 acts as a clevis such thatthe slip segment 30 mounted to slip connector 36 is pulled up and back,or radially outwardly, from a tubular positioned between slip assemblies28 as top plate 14 is raised relative to base plate 12. This movement ofslip segments 30 from the position shown in FIG. 2 engaging a tubularpositioned between slip assemblies 28 to the raised position, back andaway from a tubular by the pivoting of dual linkage slip assembly 28, isillustrated by comparison of FIGS. 1 and 2. To facilitate movement ofthe slip segment 30 from the set position engaging a tubular positionedbetween slip assemblies 28 to the raised position back and away from thetubular, base plate 12 is provided with a surface 56 for engaging theoutside surface of the slip segment 30 mounted to slip connector 36 toguide the slip segment 30 during upward and/or downward movement.

As noted above, the angled portion 37 of slip connector 36 providesadditional rotation and mechanical advantage to the retraction of theslip segment 30 from a tubular positioned between slip assemblies 28.Similarly, the positioning of the pulley 42 on top plate 14 radiallyoutwardly (relative to the tubular positioned between slip segments 30)from the pivoting connection between slip linkage 34 and top plate 14provides a mechanical advantage to the pivoting of the dual linkage slipassembly 28. Likewise, the pivotal connection between slip connector 36and slip segment 30 is positioned radially inwardly of the pivotalconnection between slip linkage 34 and top plate 14 when the slipsegment 30 engages a tubular for this same reason.

Those skilled in the art who have the benefit of this disclosure willrecognize that certain changes can be made to the component parts of theapparatus of the present invention without changing the manner in whichthose parts function and/or interact to achieve their intended result.By way of example, those skilled in the art who have the benefit of thisdisclosure will recognize that a pulley is not required for properfunction of the power slip 10 shown herein. Instead, cable 44 could passover a roller, or even a polished concave surface formed in a shoulderthat is formed in or integrally mounted to top plate 14. It will also berecognized by those skilled in the art that cable 44 need not pass overpulley 44 at all and that the length of cable 44 extending from pulley42 to slip linkage 34 could be replaced by a lever arm pivoted atapproximately the same location as the mount for pulley 42 and pivotallymounted to slip linkage 34, that is actuated by cable 44. Alternatively,a chain, cam linkage, or cam follower, can be utilized to provide thepivoting, rotational motion of the dual linkage described herein toretract the slip segments 30 from the set position to the raisedposition. All such changes, and others that will be clear to thoseskilled in the art from this description of the preferred embodiments ofthe invention, are intended to fall within the scope of the following,non-limiting claims.

1. A power slip for releasably gripping a tubular comprising: a baseplate; a top plate; one or more selectively actuated lift cylindersmounted between said base plate and said top plate for raising said topplate relative to said base plate; and at least two slip assemblies,each of said slip assemblies comprising: a slip linkage pivotallymounted to said top plate; a slip connector pivotally mounted to theslip linkage at one end and adapted at the other end for pivotallymounting to a slip segment for releasably gripping a tubular positionedbetween said slip assemblies; a pulley mounted to said top plate; and acable having one end anchored to said base plate and the other endanchored to either the slip linkage or the slip connector, or to boththe slip linkage and the slip connector, and passing over the pulley forpulling a slip segment up and back away from a tubular positionedbetween said slip assemblies when said top plate is raised relative tosaid base plate by actuating said lift cylinders. 2-12. (canceled)
 13. Apower slip for mounting to a pin drive master bushing comprising: abottom plate; a lift cylinder; a top plate supported above said bottomplate on said lift cylinder; a plurality of cables, each of said cablesbeing anchored to said bottom plate and passing over a pulley mounted tosaid top plate; a slip segment for releasably gripping a tubular, saidslip segment being mounted to a respective cable for moving betweenfirst, set and second, raised positions as said top plate is raised andlowered relative to said bottom plate by selectively actuating said liftcylinder; and said bottom plate being provided with a plurality ofhollow pins for engaging a pin drive master bushing, one or more of saidpins receiving said lift cylinder therein.
 14. The power slip of claim13 additionally comprising a tension cable for limiting movement of saidtop plate relative to said bottom plate when said lift cylinder isactuated.
 15. The power slip of claim 13 additionally comprising a sliplinkage pivotally mounted to said top plate and having said cablemounted thereto for pivoting said slip linkage relative to said topplate when said lift cylinder is actuated.
 16. The power slip of claim15 additionally comprising a slip connector interposed between said sliplinkage and said slip segment for pivoting relative to said slip linkagewhen said lift cylinder is actuated, said slip segment being mounted tosaid slip connector.
 17. The power slip of claim 16 wherein said slipconnector includes an angled portion for providing rotation andmechanical advantage to the movement of said slip segment upon actuationof said lift cylinder.